Field of the Invention
The present invention relates to a method of producing a toner particle that is used to form a toner image by the development of an electrostatic latent image that is formed by a method such as an electrophotographic method, electrostatic recording method, or toner jet recording method.
Description of the Related Art
Energy conservation has in recent years been regarded as a major technical issue for copiers, printers, and facsimile machines, and major reductions in the amount of heat applied at a fixing apparatus are desired. Thus, with regard to toners, there is strong need for the ability to undergo fixing at lower energies, or what is known as “low-temperature fixability”.
In addition, with the growing global demand for these devices, devices are required that can consistently deliver high-quality images in diverse use environments, in particular, in environments with different temperature and humidity levels. Moreover, a high durability with no decline in image quality is also required for the production of a large number of copies or prints in severe environments.
A general method for improving the low-temperature fixability of toners is to lower the glass transition temperature (Tg) of the binder resin used. However, the heat-resistant storage stability of the toner ends up being impaired when the Tg of the binder resin is just simply lowered, and it is thus quite difficult for the low-temperature fixability to co-exist in good balance with the heat-resistant storage stability.
In pursuit of having the low-temperature fixability of a toner co-exist in good balance with its heat-resistant storage stability, methods have been investigated in which a crystalline resin having an excellent sharp melt property is used for the binder resin. Crystalline polyester resins have a structure in which the polymer chains are regularly arranged and exhibit a behavior whereby they are resistant to softening in the temperature region below the melting point while undergoing sharp melting at the borderline with the melting point with a loss of viscosity. As a result of these characteristics, attention has been given in particular to crystalline polyester resins in recent years and investigations in which they are used as a toner material are being actively carried out.
However, when just the simple addition of a crystalline resin is carried out, not only can the heat-resistant storage stability of the toner deteriorate, but the crystallinity of the crystalline resin may be changed by the toner production conditions and by storage of the toner at high temperatures and the properties of the toner may then deteriorate in association with this. As a consequence, variously engineered toners have been introduced in order to exploit the properties of crystalline resins. Specifically, efforts have been made to improve the heat-resistant storage stability and suppress the changes in the degree of crystallinity induced by residence at high temperatures, by bringing about crystal growth in the crystalline resin by holding the crystalline resin for an extended period of time at a temperature below the melting point of the crystalline resin.
Japanese Patent Application Laid-open No. 2006-65015 introduces a toner production method that includes a step of storing a crystalline resin-containing toner at temperatures from 45° C. to 65° C. However, some of the toner may undergo aggregation in this toner production method due to the storage step at these temperatures. In addition, by carrying out this step as a dry method, a phenomenon is produced in which the crystalline resin present near the toner surface moves to the toner surface in association with crystal growth, and the image density and other development properties of the toner may then undergo a decline.
Japanese Patent Application Laid-open No. 2009-128652 introduces a method in which a heat treatment is performed, on a toner provided by the addition of a crystalline polyester to an amorphous polyester, at a particular temperature below the melting point of the crystalline polyester. Due to the use in the binder resin in this toner of an amorphous polyester, the crystalline polyester is compatible with the binder resin during the toner production process. Due to this, not only does the efficiency in enhancing the degree of crystallinity in the ensuing heat treatment undergo a major decline, but some of the components end up remaining compatible and a satisfactory heat-resistant storage stability may then not be obtained.
The toner production method provided by Japanese Patent Application Laid-open No. 2012-93704 includes a step of holding a toner containing a crystalline polyester resin in an amorphous polyester resin as the binder resin, at a temperature below the melting point of the crystalline resin during production by the dissolution suspension method. However, with this toner again, since the crystalline resin and binder resin are very readily blended compatibly, a satisfactory enhancement of the degree of crystallinity of the crystalline resin in the toner cannot be obtained and the low-temperature fixability cannot be made to co-exist in good balance with the heat-resistant storage stability.
Thus, as seen in the preceding, there have been a variety of efforts with regard to crystalline resin-containing toners to fully utilize the fixing performance due to the addition of the crystalline resin while suppressing the ill effects on the storability; however, a toner production method that efficiently provides favorable properties has yet to be introduced.